“I’ve spoken openly about being bullied throughout the past few years, but one thing that I’ve never been able to feel comfortable talking about was the effects that it had on my life, afterwards,” Demi tells Robin Roberts in a clip from the interview airing Friday. “I literally didn’t know why they were being so mean to me. And when I would ask them why, they would just say, ‘Well, you’re fat.’ ”

“I developed an eating disorder, and that’s kind of what I’ve been dealing with ever since,” she explained.

And at the age of 11, Demi began cutting herself to cope with emotions.

“It was a way of expressing my own shame, of myself, on my own body,” Demi explained. “I was matching the inside to the outside. And there were some times where my emotions were just so built up, I didn’t know what to do. The only way that I could get instant gratification was through an immediate release on myself.”